This invention relates generally to the de-watering of materials such as foodstuffs, and has to do particularly with a method and apparatus designed to dewater easily bruised foods such as spinach and lettuce.
The popularity of pre-cut and prepared fresh salads, which are ready-to-eat and are often packed in sealed clear plastic bags directly after the food has gone through a washing step, has led to a great increase in the quantity of product that is processed this way. The sealed packages may be individual servings or large institutional sizes. The bags extend shelf life of the product by slowing respiration (lower O2 levels) and by preventing moisture loss.
A potential problem can arise in the form of excess surface water adhering to the product after the washing step, the water subsequently appearing in the sealed bags. This entrapped water is unsightly, can make some components of the salad soggy and limp, provides a site for pathogen build-up and reduces shelf life.
Unfortunately, it is not possible to eliminate this problem merely by removing the-washing step. Washing is necessary in order to remove field soil and, if a chlorinated wash is used, to lower the spore and bacterial loads initially present. The problem of excessive water arises mainly with leafy vegetables, such as lettuce and spinach, which have large surface areas to which water drops readily adhere, although this invention is applicable to any materials that require de-watering.
At the present time, the food industry removes excess water by utilizing batch centrifuges, shakers, or tunnel dryers. Typical commercial centrifuge throughputs range from 1,000 to 6,000 kg/hr, this requiring a number of large machines. The centrifuges are usually expensive batch machines which must be loaded, brought up to speed, stopped and unloaded (which makes them labour and time intensive). Even the so-called automatic centrifugal dryers are nonetheless batch operations, improved by the provision of feed and discharge conveyors to expedite handling between spins. The large g-forces encountered can cause crushing and bruising injury to delicate products as well as increasing cell juice loss and smearing. The shakers are usually vibrating screens which can damage the product, and which, by themselves, usually do not remove enough water. A drying tunnel removes moisture by forced hot-air convection, which evaporates water as the product is continuously conveyed through the tunnel. This tends to lead to excessive dehydration of the portions that are most directly in the airflow. It is desirable to remove only the excess surface water, but not the moisture which occurs naturally within the product. Tunnels are large, slow devices limited by the evaporation rate. They are also energy-intensive, since much more energy is required for an evaporative phase change (liquid to gas) than when mechanically accelerating water off the product. Tunnels, shakers and centrifuges presently in use are often cited as bottlenecks by the industry, which has been seeking a viable alternative that is fast, simple, cheap and effective.
U.S. Pat. No. 5,501,241 is exemplary of the prior art and discloses a device adapted for batch operation, the device including a bucket-shaped container, a domed cover for the container, and a network of tubing through which compressed air is discharged in order to dry food products supported within the container. The dome-shaped cover re-directs upwardly flowing air back down toward the food product, causing certain foods (such as lettuce) to tumble in the resulting air stream. The tube apertures could also be used for washing the product, by first spraying water into the interior of the container. This device exhibits the same disadvantages inherent in all batch-operation devices: necessary stop-start operation and labour intensive.
U.S. Pat. No. 2,666,711, utilizes a concatenation of stages involving washing, immersion, repeated washing, vibrating and drying. While the disclosed apparatus is continuous and does not carry out batch operations, nonetheless the installation is needlessly complex and expensive. For example, a list of parts required would include: blowers, pumps, motors, dampers, valves, nozzles, ducts, seals, separator units, baffles, vibrators, springs, jets, water-baths, fasteners and a framework to hold it all together. As well, there is a risk that delicate food products such as spinach would tend to be bruised or crushed by contact with the vibratory portions. Crosset incorporates three leaf-washing sections upstream of the de-watering section. Crosset accomplishes de-watering by vibrating the mesh conveyor belt and by using air suction to draw the vibrated water droplets away. In the present invention, de-watering takes place by spinning the droplets off the leaves onto an internal duct wall, where they coalesce and drain away by gravity.
In view of the foregoing disadvantages and failures of prior approaches to the continuous handling of delicate foodstuffs, this invention is directed towards the provision of an apparatus for de-watering foodstuffs, such as spinach and lettuce, which is continuous, inexpensive, effective and reliable.
More particularly, this invention provides, in one aspect, an apparatus for removing liquid from the surfaces of materials, comprising:
an air-permeable transport for moving the materials along a path,
an airlift location in said path,
an air-blower for creating an upwardly moving air vortex which passes through the transport at said airlift location, raising the materials off the transport and swirling them in a vortical manner,
a conveyor for conveying the materials along a track,
a duct having an upstream end and a downstream end,
said upstream end being located above said airlift location, whereby the duct receives the swirling materials at said airlift location,
said downstream end being located above a deposit location on said conveyor, whereby the swirled materials are deposited onto the conveyor at said deposit location.
Furthermore, this invention provides, in a further aspect thereof, an apparatus for de-watering foodstuffs, comprising:
air-permeable transport means for moving the foodstuffs along a path,
an airlift location in said path,
air-blower means for creating an upwardly moving air vortex which passes through the transport means at said airlift location, raising the foodstuffs off the transport means and swirling them in a vortical manner, thereby de-watering them,
conveyor means for conveying foodstuffs along a track,
a deposit location on said conveyor means,
duct means having an upstream end and a downstream end,
said upstream end being located above said airlift location, whereby the duct means receives the swirling air and foodstuffs at said airlift location and conducts them to its downstream end,
said downstream end being located above said deposit location on said conveyor means, whereby the swirled foodstuffs are deposited onto the conveyor means at said deposit location.
Finally this invention provides, in an additional aspect, a process for dewatering foodstuffs, comprising the steps:
moving the foodstuffs along a path,
creating an upwardly moving air vortex which intersects the path, thereby raising the foodstuffs upwardly from the path while swirling them in a vortical manner,
receiving the rising, swirling foodstuffs in one end of a duct, said one end being located adjacent the path,
the other end of the duct depositing the foodstuffs on a conveyor means.